Conventionally, a hybrid vehicle, a fuel-cell vehicle, an electric vehicle and the like that travels by the driving force provided from a motor attract an attention as one approach to environmental issues. Such a vehicle has a battery mounted therein for supplying the motor with electric power. However, leaving such a battery for a long period of time with a large state of charge promotes its degradation.
In view of such an issue, Japanese Patent Laying-Open No. 2006-304393 (Patent Literature 1) discloses a power supply device including a plurality of batteries having different characteristics, that allows the batteries' characteristics to be considered to allow the batteries to be in better states to reduce their degradation. This power supply device is a power supply device externally receiving electric power and supplying external electric power consuming equipment therewith, and includes: a first electrically chargeable and dischargeable battery having a first characteristic; a second electrically chargeable and dischargeable battery having a second characteristic different from the first characteristic; a voltage adjustment means that can adjust a first voltage that is a voltage of a first voltage system having the first battery connected thereto and a second voltage that is a voltage of a second voltage system having the second battery connected thereto; a first state detection means that detects the state of the first battery; and a control means that controls the voltage adjustment means so that the first battery and the second battery communicate electric power therebetween to allow the first battery to be in a good state based on the state of the first battery, as detected by the first state detection means, when the power supply device does not receive electric power externally. The power supply device disclosed in the above publication allows a battery to be in a better state.